Magnetic blowout switch



| J. MELHART 2,936,390

MAGNETIC BLOWOUT SWITCH May 10, 1960 Filed Oct. 17, 19 58 2 Sheets-Sheet 1 INVENTOR LEONARD J. MELHART 26 BY @M/ ATTORNEY y 10, 1960 J. MELHART 2,936,390

MAGNETIC BLOWOUT SWITCH Filed Oct. 17, 1958 2 Sheets-Sheet 2 INVENTOR LEONAR D J. MELHART ATTORNEY United States Patent MAGNETIC BLOWOUT SWITCH Leonard J. Melhart, Oxon Hill, Md.

Application October 17, 1958, Serial No. 767,998

9 Claims. (Cl. 313--306) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to are discharge switches and more particularly to high current, low inductance arc discharge switches of the magnetohydrodynarnic type.

Heretofore, arc discharges have been carried out between two electrodes to break down the medium between the electrodes. In the prior art devices, the arc between the electrodes pinches down toward the axis of the space between the electrodes. The localized are produces heat which affects the electrodes and insulation and thereby limits the number of times the switch can be used with high current discharges.

The present invention is directed to an arc gap discharge switch employing an arrangement in which the arc is forced away from the switch perpendicular to the electrode axis. Thus, the switchproduces a high temperature, high velocity, shock wave directed away from the switch. Such a switch can be fired many times which far exceed the number of firings with the prior art type of air gap switches of the high current type.

It is therefore, an object of the present invention to provide a long lasting, simple, and inexpensive gap switch.

Another object is to provide a switch which is readily accessible for easy and quick adjustment of the electrode spacing or changing of the electrodes, if necessary.

Still another object is to provide a gap switch suitable for forcing the high temperature spark in the gap, as well as the metallic vapors formed during discharge, away from the electrodes, insulation, and tickler protrusions.

Yet another object is to provide a high current, low inductance switch suitable for many applications. This is accomplished because the switch conforms to the parallel plate transmission line geometry whereas the prior art devices do not.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawings, in which:

Fig. 1 shows a plan view, partly in section, of a preferred embodiment of the invention;

Fig. 2 is an illustration of the switch in an operable electrical circuit;

Figs. 3 and 4 are modifications of Fig. 1;

Fig. 5 illustrates an air gap switch suitable for producing high velocity gases;

Fig. 6 illustrates two air gap switch devices directed toward each other;

Fig. 7 illustrates an arrangement suitable for ionic propulsion devices; and

Fig. 8 illustrates an air gap device used for coating metal onto an object.

The device of the present invention is made in the form of parallel conductors separated by an insulating material. One of the conductors being continuous and the other conductor is opened and electrodes attached "ice thereto at the opened ends of the conductor to form an open air gap. The distance between the electrodes depends on the operating voltage and the delay time desired in passing current across the gap. For the purpose of minimizing inductance the switch can be constructed with plates as wide as the transmission line and tickler electrodes are provided to ionize the air in the air gap causing the main condenser bank to discharge, thereby reducing the firing time, and to uniformly distribute the current flow across the switch, thereby reducing the switch inductance. It has been demonstrated that parallel discharge across the gap will occur at the plates ionized by the ticklers. This is a unique feature of this switch and contributes to its very low inductance and high current carrying capacity. 7

Now referring to the drawings and more particularly to Fig. 1 there is illustrated a plan view of a switch made in accordance to the present invention. As shown, the switch comprises electrical conductors in the form of transmission plates 11 and 12 made of any suitable electrical conducting material, preferably copper, separated by a sheet of insulating material 13 such as mylar or any other suitable material that forms a good electrical insulator. Conductor 12 has been opened to form an air gap in the conductor and electrode plates 14 and 15, made of any suitable electrical conducting material,

" preferably brass, are connected to the ends thereof by any suitable means to provide suflicient conducting surface to pass an arc therebetween. One of the electrode plates is made adjustable through any suitable adjustable means 20 for the purpose of adjusting the air gap in accordance to the voltage used and the desired delay Teflon or Lucite is required between the air gap and back conductor 11 to Withstand the blast effect in its proximity.

For the purpose of triggering the spark gap to break down the air between the electrode plates, tickler points 17 are provided. As shown, the tickler points are supplied by coaxial cables 18 equally spaced along the stationary electrode plate. The tickler is brought into the gap close to the inside edge of electrode so that the tickler spark will jump close to the inside surfaces. This is facilitated by the opening due to electrode curvature. The outer conductor 21 of the coaxial cable connects with the electrodes at 22 and the inner conductor 23 with the insulation thereon passes through the electrode plate such .that the tickler points extend slightly into the air gap spacing.

In the form of a fiat plate switch as shown the switch is capable of repeatedly passing currents in excess of one million amperes with an inductance of less than 5 X lO henries and with a resistance of less than .004 ohm. The switch utilizes the inherent magnetic pressures associated with the high currents through the back plate on conductor 11 to force the high temperature electrically heated air, as well as metallic electrode vapors, away from the electrical insulation and the back plate conductor behind the air gap.

In operation, reference will be made to Fig. 2 which illustrates the switch connected in a suitable circuit. The circuit includes a condenser or condenser bank 25 which supplies current to a load 24 through the switch 10. As an aid in operating the switch 10, a current is applied to the tickler points by a condenser 26 through a tickler switch 27. The condensers are charged and then the tickler switch is closed, discharging condenser 26' across the tickler points and the electrode plate to produce a spark across I1 the gap. The point 17 of the tickler has an opposite polarity from the opposite electrode in order to minimize delay in initiating the break down between the main electrodes,- thus, a spark discharge across the opening, ionizes the air between the main electrodes thereby causing the main condenser to discharge across the main electrodes.

Discharge across the main electre'des produces high temperature electrically heated air, as well as metallic electrode vapors in the air gap between the electrodes. The magnetic field set up about the gap by the back conductor plate 11 forces the hot air and metallic vapors away from the insulation and plate perpendicular to the axis of the air gap. Therefore, there is no deleterious effect on the electrodes, the insulation or the electrical conductor parallel to the air gap. Since the magnetic field forces the high temperature ionized air away from the insulation, it is only necessary to increase the thickness of the insulation at the air gap only slightly thicker than the insulation normally between the conductors. Also, the magnetic field forces the metallic vapors away from the gap such that the insulation will not becom plated and cause a short circuit.

Figs. 3 and 4 illustrate modifications of the air gap switch device shown in Fig. 1. Fig. 3 illustrates the use of an air gap switch in a coaxial transmission line. As shown the outer conductor 51 is cut away and insulation 52 is removed to expose the inner conductor 53. The inner conductor is electrically opened and electrodes 54 and 55 are connected to the open ends of the inner conductor. One of the electrodes such as 55 is adapted with a tickler electrode 56 to initiate the discharge. The operation is the same as for the switch of Fig. 1 wherein the hot electrically heated gases formed by a discharge across the opening is blown out perpendicular to the axis of the conductor by the magnetic pressure of the outer conductor backing the opening in the center conductor. Additional insulation is applied to outer conductor 51 to prevent a short circuit when the arc discharge occurs.

Fig. 4- is another modification of Fig. 1 which illustrates an air gap switch suitable for a high voltage parallel plate transmission line. The gap switch is formed by opening conductor 58 and bending each end thus formed into adjacent right angles, to which terminations are fastened the electrodes 61 and 62 and separated by insulation 59 and adjustable insulation 60, the position of the adjustable insulation determines the voltage at which the switch is opened. Tickler electrode 63 is inserted through electrode 61 with the end thereof extending into the open gap to initiate the discharge of the main circuit. The protruding insulation in the switch prevents the high voltage from arcing across the gap before desired. Magnetic pressure produced in the arc discharge forces the hot gases away from the insulation to prevent damage thereto.

The devices illustrated by Figs. 1, 3 and 4 are directed to an air gap switch in a parallel transmission line in which the inherent magnetic pressures associated with the high currents forces the high temperature electrically heated air as well as the metallic electrode vapors away from the insulation between the transmission line and the electrodes. It is obvious that such a principle can be used with good results in carrying out the teaching disclosed by this application to other useful devices as shown by illustration in Figs. 5, 6, 7 and 8.

Fig. illustrates a device having parallel electrical conductors 64 and 65 separated by an insulating material 66. The electrical conductors have the end thereof in the form of an L with conductor 65 extending around the end of the insulation to form an air gap 67 between the ends of the conductors to which suitable electrodes are connected. The air gap lies directly opposite to a portion of the electrical conductor 65 which forms a leg of the L and produces a magnetic pressure about the conductor which forces the hot gases away from the gap during dis 4 charge across the gap. Such a device can be used in high velocity wind tunnels, as an ionic driven turbine by directing the gases onto a turbine wheel, or for the purpose of magnetically driving a spark into an explosive mixture for ignition of the explosive which may be a high explosive mixture, an internal combustion engine or any other desired explosive device.

Fig. 6 illustrates the use of two devices as shown in Fig. 5 which are fired simultaneously toward each other to provide an intense heat concentration at the point of intersection of the hot gases.

Fig. 7 illustrates the use of an air gap switch as an ionic propulsion mechanism. In this device the air gap switch is formed by electrodes 67 and 68 connected to the ends of conductors 69 and 79. The air gap is formed parallel to a portion of conductor '70 which is bent around to form an open eyelet and then the conductor extends around the end of insulation 71 such that the end is opposite to the end of the other conductor which extends around a portion of theeyelet. Discharge of a condenser 72 across the air gap ionizes the air in the gap and the magnetic pressure produced by the portion of the conductor opposite the air gap forces the ionized gases away from the air gap. By using trigger discharges, timing control can be devised and with a high power charging supply, a high repetition rate discharge will multiply the impetus. The force of the high temperature ionzed gas away from the device provides a propulsion force to drive the mechanism.

It has been determined that air gap switches as described above produce a temperature of about 20,000 deg. K. in the gap with an attendant shock velocity for the heated air directed perpendicular to the axis of the switch by the magnetic pressure of about Mach 20 at sea level air pressure. As the air pressure is decreased, such as obtains at higher altitudes, temperatures in the millions of degrees with shock velocities in the order of Mach 300 are achieved, and due to the magnetic insulation, damage to the switch elements is avoided.

Fig. 8 is directed to a device suitable for plating articles with a thin layer of metal, such as silver or platinum. The device is formed by parallel conductors 77 and 73 separated by an insulating material 74. One of the condoctors 77 extends around the end of the insulating material and extends towdard the other conductor. The spacing between the ends of the conductors forms an air gap switch parallel to the backing conductor 77. Electrodes 75 and 76 made of the material desired to be plated onto an object is attached to the ends of the conductors. A discharge across the air gap causes portions of the electrodes to vaporize and the vapors of the electrodes in the air gap are blown away from the gap by the magnetic pressure created by the conductor parallel to the air gap. Repeated discharges across the gap will provide coatings of the metal of any desired thickness.

In operation of the devices illustrated above, the firing time delay depends on the separation of the electrodes, the operating voltage, and the presence of a tickler electrode for initiating the discharge. An operating range of the switch can be established wherein the delay time for the switch arc discharge is reduced to 0.1 MSec. after the tickler discharge. Obviously without the tickler electrode, the firing time will not be closely controllable and the firing time will be irregular; therefore, for quick programmed firing, a tickler discharge is necessary. There are instances when controlled timing is not important and the tickler control of firing can be eliminated in all switches described, by simply increasing the voltage on the main condenser bank until the switch gap breaks down of its own accord.

Minimum inductance in the transmission lines is achieved by keeping the conductors of the switch short, widening them as much as practicable, and securing the two conductors close together while keeping the intervening insulation as thin as the over-voltage safety factor permits. This is readily seen from the formula L: 1.3 X lO' dl/w in microhenries for the inductance of a parallel plate transmission line of length, 1, width, w, and separated a distance, d, measured in centimeters.

As an example for operation of the parallel plate transmission line switch as shown in Fig. 2, the triggering electrode is supplied by a 0.01 mfd., 75 kv. capacitor and the load capacitor bank of 140 mfd. across the switch is charged to 20 kv. developing a current of over amperes. Such a load capacitor is suitable for discharging a high current for use by thermonuclear research devices or any other device which requires high currents or high voltages for operation.

'Of the devices described, that shown in Fig. 3 due to its coaxial geometry is particularly suitable for enclosure and can be operated as a vacuum switch or as a pressurized switch for the purpose of increasing a high voltage break down point for a given gap length.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An air gap switch adapted to be positioned in an electrical circuit which comprises first and second parallel electrical conductors separated by an insulating material, said first electrical conductor being continuous, said second electrical conductor having an open circuit with ends of said second conductor at the open circuit separated to form an air gap, a portion of said first conductor and said insulating material being parallel to and backing said air gap in said second conductor and said first and second conductors are adapted to be connected into load lines of said electrical circuit.

2. An air gap switch adapted to be positioned in an electrical circuit which comprises first and second parallel electrical conductors separated by an insulating material, said first electrical conductor being continuous, said second electrical conductor having an open circuit with ends of said second conductor at the open circuit separated to form an air gap, a portion of said first conductor and said insulator being parallel to and backing said air gap in said second conductor and electrodes connected to the ends of said second electrical conductor at the open circuit forming said air gap and said first and second conductors are adapted to be connected into load lines of electrical conductor having an open circuit with ends of said second conductor at the open circuit separated to form an air gap, a portion of said first conductor and said insulation being parallel to and backing said air gap, electrodes secured to the ends of said second conductor at the open circuit forming said air gap and at least one tickler electrode extending through one of said electrodes with an end thereof extending into said air gap and said first and second conductors are adapted to be connected into load lines of said electrical circuit.

4. An air gap switch adapted to be positioned in an electrical circuit which comprises first and second parallel flat plate electrical conductors separated by a sheet of insulating material, said first plate conductor being continuous, said second plate conductor having an open circuit therein with oppositely disposed ends separated to form an air gap therebetween, electrodes secured to said oppositely disposed ends to provide an air gap therebetween with an axis through said electrodes parallel to said first conductor and said first and second conductors are adapted to be connected into load lines of said electrical circuit.

5. An air gap switch as claimed in claim 4 wherein one of said electrodes is adapted to adjust the air gap spacing between said electrodes.

6. An air gap switch as claimed in claim.5 wherein the stationary electrode is provided with at least one tickler electrode.

7. An air gap switch adapted to be connected into the conductor lines of an electric circuit which comprises first and second parallel plate-like electrical conductors separated by a sheet of insulating material, said first plate conductor being continuous and adapted to be connected in one line of said electrical circuit, said second plate conductor having an open circuit therein and adapted to be connected in another line of said circuit with oppositely disposed ends at said open circuit separated to form an air gap therebetween, said first conductor and said insulation being parallel to and backing said air gap in said second conductor.

8. An air gap switch as claimed in claim 7 in which plate electrodes are connected to said second conductor at said air gap.

9. An air gap switch as claimed in claim 7 wherein one of said electrodes is provided with at least one tickler electrode.

References Cited in the file of this patent UNITED STATES EATENTS 2,043 Stearns Aug. 1, 1865 571,099 Skinner Nov. 10, 1896 963,233 Mann July 5, 1910 1,448,559 May May 13, 1923 

